This invention relates generally to the use of hydrogen gas as a fuel and is concerned with a secondary source which enables the storage and subsequent controlled liberation of hydrogen gas for use as a fuel. The invention concerns such a secondary source which is also readily adaptable to use in mobile systems.
More particularly, this invention concerns the use of lithium borohydride as such a source of hydrogen and specifically is directed toward a method of recycling the lithium borate by-product of the hydrogen generation reaction back to the lithium borohydride starting material.
As the energy squeeze continues, and at times reaches crisis proportions, increasing interest and concern is directed toward the development of new sources of energy. A most important concern is the continuing and ever increasing consumption of our limited fossil fuels with the consumption of petroleum-derived fuels being an acute concern. As the consumption of petroleum continues and in fact increases, reducing the world's limited known reserves, efforts are directed toward the development of alternative energy sources to alleviate the pressing demand for more energy. A particular concern is the enormous amount of pertroleum being burned as motor vehicle fuel and as fuel at central electric power-generating stations. An alternative fuel for these applications is especially desired in view of the enormous amount of fuel so consumed and in view of the fact that petroleum can more valuably be put to use in other products, i.e. plastics, lubricants, synthetics, etc.
One possible and highly potential alternative fuel which has been proposed and widely considered is hydrogen. In fact, proponents of the development of hydrogen as an alternative fuel have gone so far as to suggest the possibilities of a "hydrogen economy", that is, that the development of hydrogen as an alternative fuel will lead to and result in the use of hydrogen gas as a major if not the major fuel of the future. As a fuel, hydrogen gas does have potential and does offer several significant advantages, not the least of which is that it is a non-polluting fuel since its only combustion product is water vapor. This is a most important consideration in view of the equally important concern for protecting the environment.
The use of hydrogen gas as a fuel does not present any significant hurdles as many kinds of motors have been converted to run on gas and hydrogen fuel cells are widely known. Such use of hydrogen gas as a fuel is possible employing either hydrogen gas by itself or as a diluent in conjunction with natural gas. It has been proposed that hydrogen gas can be burned or used in fuel cells at individual locations, being pumped to the separate individual locations much as natural gas is today. Alternatively, hydrogen gas can be produced and stored during periods of lower power demands for subsequent burning at central power plants to produce electricity during peak power demands. Hydrogen can also be used as a motor vehicle fuel, in much the same manner as propane or butane is used at present. Various types of vehicle motors can be converted to run on the gas with common sources of the hydrogen gas being a supply of cryogenic liquid hydrogen or gas bottled under pressure.
However, since the use of pressurized bottled hydrogen or liquid hydrogen does present a number of difficult storage and handling problems, alternative materials as possible secondary sources of hydrogen gas have been extensively investigated. The difficulty with many of the alternatives and secondary sources proposed is the considerable weight penalties which are incurred with the proposed materials. This difficulty is a severe disadvantage in portable hydrogen source applications such as in motor vehicles.
The present invention was devised in response to a problem confronting a co-worker, James L. Lofthouse, who devised a method for the production of hydrogen for utilization as a fuel by storing the hydrogen in solid form as a light alkali metal borohydride and subsequently liberating the hydrogen as a gas by reacting with water. This method is the subject of a co-pending U.S patent application Ser. No. 596,554 filed July 16, 1975. It was found that because of its extremely favorable material-weight to hydrogen-production ratio lithium borohydride was a particularly favorable and advantageous secondary source of hydrogen, especially proving advantageous for use in mobile fuel systems. The lithium borohydride can be reacted with water to produce hydrogen, leaving lithium borate as a by-product. A further discussion of this method and its advantages as well as a detailed discussion of the present invention is contained in the report "Possibilities for Lithium Borohydride Recycle" by the present applicant, Evan E. Filby, Allied Chemical Corporation -- Idaho Chemical Programs Report ICP-1054, which report is incorporated herein by reference. This report was abstracted in the Nov. 30, 1974 issue of Nuclear Science Abstracts, Vol. 30, Abstract No. 28830, and is available from the National Technical Information Service, U.S. Department of Commerce, Springfield, Va. 22151.
Since the lithium borate by-product contains the valuable materials lithium and boron and it is highly desirable to avoid the waste of these materials, it is an object of the present invention to provide a method for the recycling of these materials from the lithium borate by-product.
Since it is also preferable that the boron and lithium be recycled to reconstitute the borohydride, it is also an object of the present invention to provide a method of recycling lithium borate to lithium borohydride.
It is another object of the present invention to provide a recycle scheme in which the reaction steps involved are industrially attractive.
Another object of the present invention is to provide a recycle scheme in which an acceptable energy balance exists.
Other objects and advantages of the present invention will become apparent upon reading the following description of the invention.